package com.itcam.sort.mergesort;

import java.util.Arrays;

/**
 * @author : Cammy.Wu
 * Description : 归并排序(自下而上)——非递归
 */

public class SplitSortBottomUp {
    public static void main(String[] args) {
        int[] a = {9, 5, 7, 12, 1, 3};
        System.out.println(Arrays.toString(a));
        mergeSort(a);
        System.out.println(Arrays.toString(a));
    }

    // 方法2——非递归
    public static void merge(int[] a1, int i, int iEnd, int j, int jEnd, int[] a2) {
        int k = i;
        while (i <= iEnd && j <= jEnd) {
            if (a1[i] < a1[j]) {
                a2[k] = a1[i];
                i++;
            } else {
                a2[k] = a1[j];
                j++;
            }
            k++;
        }
        if (i > iEnd) {
            System.arraycopy(a1, j, a2, k, jEnd - j + 1);
        }
        if (j > jEnd) {
            System.arraycopy(a1, i, a2, k, iEnd - i + 1);
        }
    }


    private static void mergeSort(int[] a) {
        int n = a.length;
        int[] newa = new int[n];
        // width代表有序区间的宽度，取值一次为1、2、4
        for (int width = 1; width < n; width *= 2) {
            // [left、right]分别代表待合并区间的左右边界
            for (int left = 0; left < n; left += 2 * width) {
                int right = Math.min(left + 2 * width - 1, n - 1);
                // System.out.printf("width %d [%d,%d]%n", width, left, right);
                int mid = Math.min(left + width - 1, n - 1);
                merge(a, left, mid, mid + 1, right, newa);
            }
            System.arraycopy(newa, 0, a, 0, n);
        }
    }

}
